1. Field of the Invention
The present invention relates to a catalytic converter suitable for use in automotive exhaust emission control.
2. Description of the Related Art
Catalytic converters for use in automotive exhaust gas control must have a predetermined temperature or above when operated so as to cause catalytic action. Hence, the catalyst must be heated when the temperature thereof is not sufficiently high, i.e., at the beginning of running of a vehicle.
Such techniques for heating the catalyst have been proposed in, for example, Japanese Utility Model Laid-Open No. 67609/1988. This disclosed technique is a catalytic converter comprised of a metal monolithic catalyst disposed upstream of and adjacent to a main ceramic monolithic catalyst. The metal monolithic catalyst comprises an electrically conductible metal substrate with alumina coated thereon.
However, deterioration of the catalyst such as a monolithic catalyst starts with that located upstream. In the catalytic converter disclosed in Japanese Utility Model Laid-Open No. 67609/1988, the catalytic component in the metal monolithic catalyst, which is a preheater disposed upstream of adjacent to the main monolithic catalyst, therefore deteriorates first, thereby reducing its exhaust gas conversion efficiency when the temperature of the exhaust gas is low. Furthermore, there is a possibility of the metal substrate being corroded.